Adhesive and the method of causing adherence therewith



July 13, 1943.

MELT/N6 TEMPERATURE('C) c. J. MALM TAL 2,324,097

ADHESIVE AND METHOD OF CAUSING ADHERENCE THEREWITH Filed Nov. 10, 1939 K COMPAR/SO/Y OFMELT/IYG TEMPERATURES 0F FATTY ACID ES TERS OECELLULOSE 4- s a /0 /2 /4 -/a /6 NUMBER OF CARBON ATOMS IN THE ACID OF THE SIMPLE FATTY/467D ESTER OFCELLZ/LOSE CARL J MAL/ 60R00/v Q /'//A TT INVENTORS ATT NEYS Patented July 13,1943- ADHESIVE AND THE NIETHOD OF CAUSING ADHERENCE THEREWITH Carl J. Malm and Gordon D. Hiatt, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application November 10, 1939, Serial No. 303,870

3 Claims;

This invention relates to an adhesive comprismg a cellulose ester substantially all of the acyl of whichconsists of saturated fatty acid groups of 6 to 14 carbon atoms. This invention also relates to the method of, sticking materials together by means of this adhesive in which a melting temperature is applied.

Heretofore in the sticking together of materials either the adhesive required a long time to set, has decomposed upon aging or has exhibited tackiness when warm. For instance ordinary glue or paste must be allowed to set before the Joined materials can be handled. Shellac is.unsuitable because it becomes insoluble and unworkable upon aging. Resin compositions are tacky over a wide temperature range and units thereof stick together or to other materials when stored for any length of time under normal summer conditions. 1

An object of our invention is to provide an adhesive material which makes possible instant cementing of materials and quick setting of the adhesive upon slight cooling. Another object of our invention is to provide an adhesive material which may be stored in sheet form in contact with other sheets, with paper or other materials without sticking. A further object of our invention is to provide an adhesive material which retains its properties over a long period of time. A still further object of our invention is to provide a method of joining materials in which a permanent union is rapidly accomplished. Other objects will appear herein. I

We have found that for the rapid uniting of materials it is desirable that the adhesive or bonding material soften at a temperature somewhat above those met with under ordinary conditions but that its softening point be sufiiciently sharp to eliminate tackiness and to make unnecessary' the use of high temperatures. We have found that cellulose esters substantially all of the acyl of which consists of fatty acid groups of 6-14 carbon atoms are eminently suitable for the rapid cementing of materials. These esters soften and form an effective seal at approximate= ly 100 C. under moderate pressure. When the temperature is lowered slightly such as to 70 C. the adhesive hardens forming a permanent bond without any tackiness or danger of slipping. We have found that these esters melt sharply at approximately 100 C. to form a viscous bonding material which stays in position and with but small diminution of temperature forms an excellent bond;

The cellulose esters which are suitable may be the simple esters including partially hydrolyzed products or they may be mixed esters providing in-every case that substantially all of the acyl of the ester consists of fatty acid groups of 6-14 carbon atoms. The cellulose esters of fatty acid groups of less than 6 carbon atoms are not as desirable for this purpose due to considerably higher melting points. The cellulose esters of fatty acids of more than 14 carbon atoms such as cellulose stearate or palmitate are less desirable than those specified because of their low tensile strength and bonding power and because of their tendency ,to become thin and run when subjected to heat and pressure. It is only the cellulose esters of fatty acids of 6-14 carbon atoms that we have found to be eminently suitable for adhesive materials in accordance with our invention.

The drawing illustrates the pronounced difference between the simple cellulose esters of a 5- carbon fatty acid and of a 6-carbon fatty acid.

The points designated on the graph designate the melting points of individual esters and are representative in each case. Because of this difference in melting points, the cellulose esters of fatty acids of more than 5 carbon atoms are eminently suitable for an adhesive sheet in which heat-sealing is featured.

One of the principal uses of our invention is in the making of dry mounting tissue. This is used in the photographic trade to mount pictures without the use of any liquid. By coating tissue, glassine or the like with our adhesive, 8. dry mounting tissue is obtained which will readily bind paper, cardboard or the like together by applying pressure and a melting temperature thereto. Any suitable solvent such as iso-propyl alcohol. may be employed to form. a coating of the ester on the tissue or glassine. As all of these cellulose esters melt below C. the degree of heat used need not be great, yet but slight cooling results in a permanent non-tacky bond.

Cellulose caproate or caprate, which because of low cost show the greatest promise at the present time, may be conveniently prepared by reacting upon cellulose with chloracetic anhydride, chloracetic acid and from two-thirds of the theoretical up to the theoretical amount of caproic or capric acid. As caproic acid and capric acid have limited solubility in water any excess is difilcultto remove from the. ester formed and therefore it is preferable that not more than the amount which actually combines with the cellulose be used.

Our adhesive may be employed either in the A cellulose laurate containing 76.9% lauryl was dissolved in ethylene dichloride-methyl alcohol (9 1) and the solution was flowed out onto a filmforming surface forming a sheet of skin. The skin was dried for 18 hours at 55 C. Strips of this material were placed between photostat paper and a paper, support upon which it was to be mounted. The whole was pressed together at a temperature of approximately 100 C. to properly seal the paper to the support. could be handled while the paper was still warm.

Example II Glassine paper was coated by dipping it into a 20% acetone solution of an unhydrolyzed cellulose caproate. The paper was dried for 4 hours at 55 C. This coated material was found to firmly seal photographic paper to a paper support at a temperature of 100 C. and under an average pressure of 2 lbs. per square inch. Under the same conditions this material was found to be suitable to seal a transparent photographic positive on its gelatin side to a paper support.

Example III A dry mounting tissue was prepared by applying to glassine paper a thin coating of a stable low-viscosity cellulose caprate in molten condition from a hopper. A blade was used to spread and smooth the coating while still in a soft condition. Instead of a blade, an air brush can be used for spreading and smoothing the layer. As the coating cools it solidifies rapidly and can be handled shortly after the application of the coat ing.

As pointed out above one of the advantage of 7 our adhesive is its absence of tackiness up to temperatures of 55-60 C. As a consequence this material may be stored under ordinary conditions without sticking to other materials with which it is in contact. The storing qualities of an adhesive sheet may be tested by laying two sheets of the material or a tissue coated therewith together between paper liners and subjecting the sheets to a pressure of 1 lb. per square inch at The bond formed 55 C. for 2 hours. Sheets having good storing qualities must not stick together or to the paper about them.

We have found that sheets of our adhesive when subjected to this test of the storing qualities of an adhesive sheet do not stick to each other or to paper in contrast to other adhesives of low melting point such a resin compositions or highly plasticized cellulose esters.

Our adhesive materiaLmay be coated on any sheeting having a melting point sufficiently high so that it is not softened by the heat-sealing of the adhesive, such as glassine paper, cloth, tissue, ordinary paper, Cellophane, parchment paper, gelatin, unplasticized cellulose lower fatty acid ester sheeting, metal foil, etc. By thus coating sheet material a highly useful wrapping material is obtained which may be sealed about an article merely by applying heat at the points where adhesion is desired. For example aluminum foil may be coated with a cellulose ester substantially all of the acyl of which is fatty acid, groups of 6-14 carbon atoms to form a wrapping material which can be wrapped around an article and heat sealed to form a covering which i permanent as long as desired. If desired dye or coloring material and/or a small proportion of wax such as paraffin might be incorporated in our adhesive. Our adhesive may be employed to cement together wood, metal, leather or any material which is unaffected by the melting temperature used.

Some of the cellulose esters eminently suitable in accordance with our invention in addition to those already disclosed are cellulose caprylate, cellulose myristate and cellulose heptylate. The cellulose esters which may be used include both those substantially fully esterified and those which are only partially esterified such as those in which approximately two-thirds or more of the hydroxyl groups are satisfied by fatty acid groups of 6-14 carbon atoms.

We claim:

1. An adhesive sheet comprising a capric acid ester of cellulose.

2. A method of cementing'material together which comprises placing cellulose caprate sheeting between the materials to be joined, pressing the materials together while applying suflicient heat to soften the cellulose ester and holding the material together until the temperature has dropped sufficiently for the cellulose caprate to harden.

3. A photographic dry mounting tissue consisting of paper coated on both sides with a capric acid ester of cellulose.

CARL J. MALM. GORDON D. HIATT. 

